/*
 * This file is part of Hadoop-Gpl-Compression.
 *
 * Hadoop-Gpl-Compression is free software: you can redistribute it
 * and/or modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation, either version 3 of
 * the License, or (at your option) any later version.
 *
 * Hadoop-Gpl-Compression is distributed in the hope that it will be
 * useful, but WITHOUT ANY WARRANTY; without even the implied warranty
 * of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with Hadoop-Gpl-Compression.  If not, see
 * <http://www.gnu.org/licenses/>.
 */
package com.hadoop.mapreduce;

import java.io.IOException;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FSDataInputStream;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.io.compress.CompressionCodec;
import org.apache.hadoop.io.compress.CompressionCodecFactory;
import org.apache.hadoop.mapreduce.InputSplit;
import org.apache.hadoop.mapreduce.RecordReader;
import org.apache.hadoop.mapreduce.TaskAttemptContext;
import org.apache.hadoop.mapreduce.lib.input.FileSplit;
import org.apache.hadoop.util.LineReader;

/**
 * Reads line from an lzo compressed text file. Treats keys as offset in file
 * and value as line.
 */
public class LzoLineRecordReader extends RecordReader<LongWritable, Text> {

    private long start;
    private long pos;
    private long end;
    private LineReader in;
    private FSDataInputStream fileIn;

    private final LongWritable key = new LongWritable();
    private final Text value = new Text();

    /**
     * Get the progress within the split.
     */
    @Override
    public float getProgress() {
        if (start == end) {
            return 0.0f;
        } else {
            return Math.min(1.0f, (pos - start) / (float) (end - start));
        }
    }

    public synchronized long getPos() throws IOException {
        return pos;
    }

    @Override
    public synchronized void close() throws IOException {
        if (in != null) {
            in.close();
        }
    }

    @Override
    public LongWritable getCurrentKey() throws IOException, InterruptedException {
        return key;
    }

    @Override
    public Text getCurrentValue() throws IOException, InterruptedException {
        return value;
    }

    @Override
    public void initialize(InputSplit genericSplit, TaskAttemptContext context) throws IOException, InterruptedException {
        FileSplit split = (FileSplit) genericSplit;
        start = split.getStart();
        end = start + split.getLength();
        final Path file = split.getPath();
        Configuration job = context.getConfiguration();

        FileSystem fs = file.getFileSystem(job);
        CompressionCodecFactory compressionCodecs = new CompressionCodecFactory(job);
        final CompressionCodec codec = compressionCodecs.getCodec(file);
        if (codec == null) {
            throw new IOException("Codec for file " + file + " not found, cannot run");
        }

        // open the file and seek to the start of the split
        fileIn = fs.open(split.getPath());

        // creates input stream and also reads the file header
        in = new LineReader(codec.createInputStream(fileIn), job);

        if (start != 0) {
            fileIn.seek(start);

            // read and ignore the first line
            in.readLine(new Text());
            start = fileIn.getPos();
        }

        this.pos = start;
    }

    @Override
    public boolean nextKeyValue() throws IOException, InterruptedException {
    //since the lzop codec reads everything in lzo blocks
        //we can't stop if the pos == end
        //instead we wait for the next block to be read in when
        //pos will be > end
        while (pos <= end) {
            key.set(pos);

            int newSize = in.readLine(value);
            if (newSize == 0) {
                return false;
            }
            pos = fileIn.getPos();

            return true;
        }

        return false;
    }
}
